Device for welding plastic films

ABSTRACT

Devices for cross-welding or cross-separating welding plastic films ( 2 ) are used in a manner known per se in machines for producing bags, said devices comprising a welding roller ( 3 ) and a heated welder terminal ( 4 ) which can be moved reciprocally and between which the plastic films ( 2 ) are guided for welding. According to the invention, the welding roller ( 3 ) is covered by a continuous belt ( 5 ).

CROSS REFERENCE TO RELATED APPLICATION

This application is a national stage of PCT/EP02/10177 filed 11 Sep.2002 and based upon German application 101 51 576.6 filed 23 Oct. 2001under the International Convention.

TECHNICAL FIELD

The invention relates to a device for cross-welding orcross-separation-welding in the production of bags, pouches and the likefrom plastic film on a bag-making machine.

STATE OF THE ART

It is known in practice to provide machines for the transverse weldingor cross-welding of plastic film or for the transverse separationwelding or cross-separation-welding of plastic films. In these cases atleast two superposed horizontal film layers are welded together. Whilethis can apply as well to a single film which is folded in alongitudinal direction and thus lies doubled up, in the followingdescription, at least two plastic films will always be referred to.

Note further that additional film layers can be welded during thewelding operation so that three film layers or more can lie one aboveanother during a welding process.

When the weld seam is to extend transversely to the travel direction ofthe plastic film, one can speak of transverse welding or cross-welding.When the cross-welding occurs simultaneously with separation of bag or apouch from the remainder of the film, in this weld process, one isdealing with a transverse separation welding orcross-separation-welding.

In the publication DE 19 10 598 A1, a cross-welding, especially across-separation-welding is described. The welding device is comprisedbasically of a heated welding beam and a welding roll or drum. The filmsto be welded are disposed between the welding drum or roll and thewelding beam. For welding, the welding beam is pressed against thewelding roll. The welding roll is preferably rubber jacketed.

Since in the welding of plastic film the heated plastic can adhere tothe welding roll and the welded bag and/or the welded plastic film canremain hanging on the welding roll, the fabrication process can bedisturbed. For that reason, the welding roll is coated on its surfacewith PTFE (Teflon) polytetrafluoroethylene. The PTFE has not only goodslidability properties but also a limited adhesion. For that reason onlyno plastics remain adherent to the PTFE even if they are heated bywelding.

As the heated welding beam is lowered onto the plastic foils during thewelding process, its welding edge presses somewhat into the PTFE coatingand into the rubber jacket lying therebelow and which, for example, iscomposed of a silicone. When the welding beam is withdrawn after thewelding process again from the welding rolls, the rubber jacket and thePTFE coating spring back. It has however been found that with thepassage of time the PTFE coating can develop folds. The result is areduction in the quality of the weld seams and a reduction in the lifeof the welding beam. Because of the fold formation in the PTFE, the PTFEcovering which is adhesively bonded to the jacket becomes loose and mustbe replaced by a new one. This gives rise to production interruptionswhich are associated with cost.

OBJECT OF THE INVENTION

It is therefore an object of the invention to provide a device forcross-welding or for cross-separation-welding which avoids the drawbacksof the state of the art or reduces them.

SUMMARY OF THE INVENTION

According to the invention no backing which ensheaths the welding rollis required on the welding roll but a continuously traveling belt restsupon the welding roll. It has been found that in this way the foldformation can be reduced and the quality of the weld seams improved.

Additionally it is advantageous that the belt according to the inventiondoes not have to be replaced as often as with the ensheathing backing orjacket with the state of the art.

It is advantageous when the belt is composed at least is on its outersurface of PTFE (Teflon). In this manner the heated plastic is readilyreleased or does not adhere to the belt initially.

Since the welding roll on its outer diameter has a rubber/siliconejacket and exactly this outer surface contributes to stiffness, thewelding roll may have insufficient bending strength especially when itis required to span large working widths. The inner metallic core of theweld roll is then not able to provide support with sufficient bendstiffness. The welding pressure of the welding beam upon the weldingroll can then produce a nonparallel welding gap. In an advantageousconfiguration of the invention, the welding roll is supported by abracing roll along its side opposite the press gap. In this manner apossible bending of the welding roll is counteracted.

The welding roll and the bracing roll are journaled at their ends inbearing plates and guided therein so that these bearing plates willalways maintain a defined parallel position with respect to one anotherby means of a traverse. The traverse extends through the loop of thebelt which is advantageous since it utilizes the space available in theloop.

An advantageous refinement of the invention is also the arrangement of abracing or backup roll in the loop of the belt whereby the bracing rollis arranged substantially parallel to the welding roll, i.e. the rollscan have parallel axes. This bracing roll holds the belt taut so that nofolds or irregularities can be formed in the belt. In addition, the beltis reliably guided by the bracing roll. In order to hold the belt taut,even with an increase in its length in the peripheral direction, it isadvantageous for the bracing roll to be spring-loaded.

BRIEF DESCRIPTION OF THE DRAWING

The invention is described below in greater detail based upon FIG. 1. Itshows:

FIG. 1 a cross section through a welding tool.

MODE OF CARRYING OUT THE INVENTION

In FIG. 1 a welding tool 1 can be seen for the cross welding or crossseparation welding. A welding beam 4 (broken away at 17) and a weldingroll 3 are the significant components of the welding device 1. Duringthe welding, plastic foils are engaged between them. In the embodimentshown the welding beam has a movement 12 from top to bottom and thereverse. In another configuration of the invention, the welding roll 3can also be moved against the welding beam 4.

According to the invention, the welding roll 3 is looped by a belt 5.The belt 5 lies upon a silicone jacket 11 of the welding roll 3.

The belt 5 is endless and is formed without abutting edges andconstitutes therefore an endless loop. For guiding and tensioning thebelt 5, within the loop a pair of tensioning rollers 6 are provided inparallel-axis relationship in the loop. Preferably a belt of PTFE(Teflon) which has been reinforced with fibers or with a fabric of glassor aramid, is used.

To brace the welding roll 3, a backing roll 7 is disposed along its sideopposite that provided with the welding beam 4 and which rolls in theopposite rotational sense against the welding roll 3. The backup orbracing roll 7 is journaled in bearing plates, not shown here, like thewelding roll 3 and the belt-tension rolls 6. With a predeterminedpressing of the backup or bracing roll 7 against the welding roll 3, itcan be ensured that the welding gap will remain parallel during thepressing of the welding beam against the welding roll 3.

Within the loop of the belt 5 a traverse 8 is also disposed. Thistraverse 8 interconnects the bearing plates which have here not beenshown. To enable the traverse 8 to provide as much stiffness aspossible, the right upper corner and the left upper corner of thetraverse 8 are extended upwardly. To increase the stiffness of thetraverse 8 it is also conceivable to extend the left lower and the rightlower corners downwardly.

In the welding of plastic film, plastic residues can remain suspendedfrom the belt 5. For this reason a wiper is provided in the form of awiping blade 15 forming part of a wiper arrangement 9 juxtaposed withthe belt 5. The wiper blade 15 contacts the belt 5 in an unsupportedregion so that the belt 5 can yield under the pressing force of thewiper blade 15.

Since the belt 5 can yield in the peripheral direction under themechanical and/or thermal stresses, the belt 5 is tensioned by means ofa tension roller 6. It is advantageous to spring-load the bearings ofthe tension roller 6, for example by a coil spring or a pneumaticcylinder. In that case a manual adjustment of the tension roller 6 byservice personnel is rendered superfluous.

In FIG. 1 the belt 5 has a brush device 10 juxtaposed therewith. Thisbrush device 10 is formed as a brush roller. By rotation of the brushroller possibly adhering plastic residues can be better removed from thesurface of the belt 5 than when the brush arrangement 10 is only astationary brush element.

1. An apparatus for cross welding or cross separation welding of plasticfilm for a machine for making bags and pouches, comprising: a weldingbeam; and a support roller juxtaposed with the welding beam forsupporting the plastic film for welding by said beam as said film passesbetween said roller and said beam, said roller and said beam beingmovable relative to one another for welding said film; a jacket ofsilicone on said roller; and an endless belt of a synthetic resinmaterial passing around said roller and interposed between said jacketand said film.
 2. The apparatus according to claim 1 at least anoutermost surface of the belt is composed of polytetrafluoroethylene. 3.The apparatus according to claim 2 wherein the belt is made ofpolytetrafluoroethylene reinforced with fibers or fabric of glass oraramid.
 4. The apparatus according to claim 1 wherein the roller issupported on a side opposite the welding beam by a packing roller. 5.The apparatus according to claim 1 characterized in that a transversepasses through a loop formed by a belt.
 6. The apparatus according toclaim 1, further comprising a stripper wiper bearing against an outersurface of the belt.
 7. The apparatus according to claim 1 wherein thebelt also passes around a tension roller.
 8. The apparatus according toclaim 7 wherein the tension roller is spring loaded.
 9. The apparatusaccording to claim 1 wherein a brush arrangement is juxtaposed with thebelt.
 10. The apparatus according to claim 9 wherein the brusharrangement is configured as a rotating brush roller.